In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited onto or removed from a substrate surface. Thin layers of conducting, semiconducting, and dielectric materials may be deposited onto the substrate surface by a number of deposition techniques. Deposition techniques common in modern microelectronics processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP).
As layers of materials are sequentially deposited onto and removed from the substrate, the uppermost surface of the substrate may become non-planar and require planarization. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide a level surface for subsequent levels of metallization and processing.
Chemical-mechanical planarization, or chemical-mechanical polishing (CMP), is a common technique used to planarize substrates. CMP utilizes a chemical composition, typically a slurry or other fluid medium, for selective removal of material from the substrate. In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad is moved relative to the substrate by an external driving force. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate by the relative movement of the pad and the substrate typically is further aided by the chemical activity of the polishing composition and/or the mechanical activity of an abrasive suspended in the polishing composition.
The ability to polish tantalum, copper, and other metal layers is hampered by the presence of a surface metal oxide layer, typically 10-50 angstroms thick depending on the deposition technique. The surface metal oxide layer has a different composition, and thus different chemical and mechanical properties, as compared to the bulk metal layer. The sacrificial metal oxide layer must be removed in order to achieve polishing of the bulk metal layer, but the chemical activity of the polishing composition and/or the mechanical activity of the abrasive may be ineffective on either the surface metal oxide layer or the bulk metal layer, leading to inefficient polishing.
Typically, polishing compositions with high solids or abrasive content quickly remove the surface metal oxide layer while polishing compositions with low solids content leave the metal oxide layer intact, yielding no bulk removal of metal. Short induction times, i.e., the time required to remove the surface metal oxide layer, are achieved with polishing compositions comprising >5 wt. % of abrasive, based on the total weight of the composition. However, high solids content can produce defects on the surface of the substrate that can negatively impact the performance of any integrated circuit layer manufactured from the substrate. Furthermore, polishing compositions containing a high solids content are less colloidally stable and are more expensive to produce.
A need therefore remains for a chemical-mechanical polishing composition that is capable of polishing a metal containing substrate with a relatively lower solids content while maintaining a short induction time for removing the surface metal oxide layer of the substrate. The invention provides such a chemical-mechanical polishing composition and related method of using the same to polish a metal substrate. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.